A SIMPLIFIED RECORDING POTENTIOMETER

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Abstract
A recording potentiometer well adapted for the study of many physiol. factors is described. It is constructed of standard radio parts and is a self-balancing, modified Wheatstone bridge controlled by photocells, thyratron tubes, galvanometer, motor, etc. It has functioned satisfactorily with bridge values as low as 80 microvolts but is usually run with a minimum of 2-3 millivolts. A single sensitivity dial adjusts these low bridge values up to a volt or more for full scale. With well balanced thyratron tubes, AC line voltages are almost without effect. Speed of travel of recording paper and speed of recording on paper can be set within broad limits. With low bridge values measurements can be made in circuits with resistances even as great as megohms in series with the unknown. Mechanically the instrument is simple to construct and very reliable in action. This recorder has been used to measure light, temp., humidity, polarigraphic analysis, etc. One microampere is sufficient to give full scale (200 mm.) deflection with 2.5 millivolt bridge. The instrument is enclosed in a cabinet 7 1/2 X 8 X 12[imagae], weighs 22 lbs., and costs about $50.00 for materials. Full sized blueprints and detailed specifications and instructions are available from the author.

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